A knee bolster is disposed ahead of a knee of a passenger sitting on a front seat of a vehicle and has a function of protecting the knee of the passenger by plastically deforming itself when the vehicle hits something head-on. Patent Literature 1 discloses a knee bolster formed of a blow-molded body. This blow-molded body is mounted on a mounting target by inserting mounting claws disposed on the back surface into mounting holes formed in the mounting target.